[colug-432] dropbox clone

[Scott Merrill]

On Thu, Jul 28, 2011 at 9:30 AM, Steven Lefevre <lefevre.10 at osu.edu> wrote:
> On Thu, Jul 28, 2011 at 8:23 AM, Scott Merrill <skippy at skippy.net> wrote:
>
>> If you don't want to manage the server end, Dropbox remains a very
>> good product. If your data is sensitive, you should encrypt it
>> yourself before uploading it to Dropbox. TrueCrypt and GPG are good
>> solutions for this.
>
> I assume these services do incremental backups for the most part.
>
> If you have an encrypted volume, and you change its contents, can you
> do an differential backup, or does that file change so much

Many of these services deal with synchronization at the block level,
rather than the file level. SpiderOak specifically addresses this in
their FAQ:
   https://spideroak.com/whyspideroak
   https://spideroak.com/faq/questions/7/does_spideroak_backup_the_whole_file_every_time_it_changes/

Dropbox does the same:
   https://www.dropbox.com/help/8

> In other word, suppose I have a 1 GB encrypted file that I back up on
> an online service. I open the volume with truecrypt, and change a few
> lines in a plain text file. How different is the encrypted file? Can
> it be backed up against the existing backup file incrementally?

You decrypt a file, make your changes, and then re-encrypt the file.
Dropbox and SpiderOak and similar providers will look at the changed
blocks in that file and transmit them to the server. Only the changed
blocks are sent, but it's conceivable that _all_ the blocks have
changed, resulting in a complete transfer of the full file.